Zantac Mechanism of Action





Zuellig Pharma
Full Prescribing Info
Pharmacology: Pharmacodynamics: Mechanism of Action: Ranitidine is a specific, rapidly acting histamine H2-antagonist. It inhibits basal and stimulated secretion of gastric acid, reducing both the volume and the acid and pepsin content of the secretion.
Pharmacodynamic Effects: Ranitidine has a relatively long duration of action and so a single 150 mg oral dose effectively suppresses gastric acid secretion for 12 hours.
Clinical evidence has shown that oral ranitidine combined with amoxicillin and metronidazole eradicates Helicobacter pylori in approximately 90% of patients. This combination therapy has been shown to significantly reduce duodenal ulcer recurrence. Helicobacter pylori infects about 95% of patients with duodenal ulcer and 80% of patients with gastric ulcer.
Pharmacokinetics: Absorption: Following oral administration of 150 mg ranitidine, maximum plasma concentrations (300 to 550 ng/mL) occurred after 1-3 hours. Two distinct peaks or a plateau in the absorption phase result from reabsorption of drug excreted into the intestine. The absolute bioavailability of ranitidine is 50-60%, and plasma concentrations increase proportionally with increasing dose up to 300 mg.
Absorption of ranitidine after i.m. injection is rapid and peak plasma concentrations are usually achieved within 15 minutes of administration.
Distribution: Ranitidine is not extensively bound to plasma proteins (15%), but exhibits a large volume of distribution ranging from 96 to 142 L.
Metabolism: Ranitidine is not extensively metabolised. The fraction of the dose recovered as metabolites is similar after both oral and i.v. dosing; and includes 6% of the dose in urine as the N-oxide, 2% as the S-oxide, 2% as desmethyl ranitidine and 1 to 2% as the furoic acid analogue.
Elimination: Plasma concentrations decline bi-exponentially, with a terminal half-life of 2-3 hours. The major route of elimination is renal. After i.v. administration of 150 mg 3H-ranitidine, 98% of the dose was recovered, including 5% in faeces and 93% in urine, of which 70% was unchanged parent drug. After oral administration of 150 mg 3H-ranitidine, 96% of the dose was recovered, 26% in faeces and 70% in urine of which 35% was unchanged parent drug. Less than 3% of the dose is excreted in bile. Renal clearance is approximately 500 mL/min, which exceeds glomerular filtration indicating net renal tubular secretion.
Special Patient Populations: Patients over 50 years of age: In patients over 50 years of age, half-life is prolonged (3-4 hours) and clearance is reduced, consistent with the age-related decline of renal function. However, systemic exposure and accumulation are 50% higher. This difference exceeds the effect of declining renal function, and indicates increased bioavailability in older patients.
Toxicology: Preclinical Safety Data: Non-clinical data revealed no special hazard for humans based on conventional studies of safety pharmacology, repeated-dose toxicity, genotoxicity, carcinogenic potential and toxicity to reproduction and development.
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